Conformal microwave array (CMA) applicators for hyperthermia of diffuse chest wall recurrence

Abstract

Purpose This article summarizes the evolution of microwave array applicators for heating large area chestwall disease as an adjuvant to external beam radiation, systemic chemotherapy, and potentially simultaneous brachytherapy. Methods Current devices used for thermotherapy of chestwall recurrence are reviewed. The largest conformal array applicator to date is evaluated in four studies: i) ability to conform to the torso is demonstrated with a CT scan of a torso phantom and MR scan of the conformal waterbolus component on a mastectomy patient; ii) Specific Absorption Rate (SAR) and temperature distributions are calculated with electromagnetic and thermal simulation software for a mastectomy patient; iii). SAR patterns are measured with a scanning SAR probe in liquid muscle phantom for a buried coplanar waveguide CMA; and iv) heating patterns and patient tolerance of CMA applicators are characterized in a clinical pilot study with 13 patients. Results CT and MR scans demonstrate excellent conformity of CMA applicators to contoured anatomy. Simulations demonstrate effective control of heating over contoured anatomy. Measurements confirm effective coverage of large treatment areas with no gaps. In 42 hyperthermia treatments, CMA applicators provided well-tolerated effective heating of up to 500cm2 regions, achieving target temperatures of Tmin=41.4±0.7°C, T90=42.1±0.6°C, Tave=42.8±0.6°C, and Tmax=44.3±0.8°C as measured in an average of 90 points per treatment. Summary The CMA applicator is an effective thermal therapy device for heating large-area superficial disease such as diffuse chestwall recurrence. It is able to cover over three times the treatment area of conventional hyperthermia devices while conforming to typical body contours.

Hypofractionated re-irradiation of large-sized recurrent breast cancer with thermography-controlled, contact-free water-filtered infra-red-A hyperthermia: a retrospective study of 73 patients

“…Such lesions have required multiple sequential treatments of smaller regions ("patchwork technique") [5] or a multiple array antenna system. There have been numerous efforts to develop larger conformal microwave array (CMA) applicators [6]. A contact free heating technique may have general advantages for the delivery of thermal energy to large superficial areas as well as for the patients' compliance, especially in cases of touchsensitive, ulcerated and/or bleeding lesions.…”

Thermoradiotherapy planning: Integration in routine clinical practice

“…Because the effect of HT is no longer tumour selective when given simultaneously with RT, an increase in therapeutic ratio can only be obtained when the volume where RT and HT are given simultaneously can be geometrically restricted to the macroscopic tumour itself. Superficial and intracavitary HT equipment suitable for simultaneous RT + HT has become available [69][70][71][72] and is clinically applied [73], but such a good delineation is challenging for HT at deep-seated tumour locations as heating in normal tissue in the vicinity of the heated tumour region cannot be avoided due to heat conduction and blood flow, even when well-controlled high resolution HT techniques are used. The tumour delineation must therefore come primarily from RT and image-guided radiotherapy techniques which permit a very precise dose control and TRTP could be used to devise an optimal combination of RT and HT treatment plans achieving high TER in tumour tissue while keeping TER in normal tissue low, even when RT and HT are given simultaneously.…”

Design of a compact antenna with flared groundplane for a wearable breast hyperthermia system

“…A lightweight and wearable system would avoid uncomfortable breast compression and follow patient breathing and motion, allowing patient postural changes during the treatment, thereby improving comfort [30], facilitating treatment persistency, and therapeutic adherence [29]. The wearable device may contribute towards delivering hyperthermia treatments in a repeatable manner over the course of several radiation and/or chemotherapy fractions.…”

“…These trials indicated significant correlation between tumour depth and complete response rate; tumours located at depths more than 2 cm from the skin yielded poor results [13]. Furthermore, drawbacks of these waveguides are their large dimensions, weight, comfort level, limited adaptability for individual patient treatments, and the limited spatial control of energy deposition [15,16].…”

“…An ergonomically shaped and wearable system in close proximity to the breast would offer enhanced energy deposition, reduced power requirements, and increased comfort, which would facilitate treatment delivery, improve therapeutic adherence and patient treatment persistence [29]. Stauffer et al [30] developed a conformal array of microstrip antennas for hyperthermia treatment of large surfaces with superficial chest wall disease (520 mm depth). Compared to waveguide technologies, this approach significantly improves patient comfort and provides enhanced control of power deposition patterns over large treatment areas.…”